PROJECT SUMMARY Waterpipe tobacco smoking is prevalent among young adults in the United States with up to 40% college students reporting waterpipe use in the past year. Its increasing popularity of is partly caused by the misperception that waterpipe smoking is safe or at least less harmful than other forms of tobacco smoking. However, waterpipe mainstream smoke yields of many of the listed harmful and potentially harmful constituents of tobacco products and tobacco are 10-100 times those observed for a cigarette. The Food and Drug Administration (FDA) mandates that packages of WP tobacco carry a text-only message about the addictiveness of nicotine. However, the effectiveness of this mandate is limited because previous research suggests that graphic warning labels are more effective, and because WP smokers will not interact with the tobacco package in the social venues where most WP smoking is done. These limitations are addressed by the overarching objective of the parent grant to investigate the impact of the placement of text-only or graphic- with-text health warning labels on the WP itself on smoking behavior. The proposed supplement research will complement the parent grant by investigating whether any changes in participants? smoking behavior will also result in measurable changes in biomarkers of potential harm. This will be done by determining the effect of the presence of the warning label on waterpipe in laboratory smoking sessions on changes in lung function and genotoxicity in 1) the short-term across the smoking sessions, and 2) over the long-term 3-months after the laboratory interventions. The research proposed in the supplement will increase our understanding of the potential health effects of WP smoking under experimental conditions and the impact of warning labels on reduction and/or cessation of WP smoking and the related health benefits. The proposed supplement addresses FDA research priority areas of Communications and Toxicity because it seeks to determine effective communications to the public and vulnerable populations about the health effects of WP smoking, and will provide quantitative data relating WP puffing behavior and biomarkers to assess harm or toxicity.